Patent GB-1312071-A (GB)
Title: Apparatus for detecting the position of a beam welding point and  the welding joint of a workpiece to be welded
IPC: B23K26/04
Filed: 1970-03-24
Abstract: 1312071 Welding by fusion VEREINIGTE FLUGTECHNISCHE WERKE - FOKKER GmbH 24 March 1970 [26 March 1969] 14264/70 Heading B3R [Also in Divisions G1 G3 H1 and H4] In electron beam welding, to determine both the position of a beam welding point (movable, e.g. due to magnetic influence) and of the joint, light rays from the point and joint are optically intercepted and transmitted to electro-optical transducers from which are derived output signals proportional to the positions of the point and joint from desired datum positions. Beam welding point position determination.- In the electron beam apparatus of Fig. 1, a light beam 11 from the electron beam welding point 10 is reflected by a mirror 12 through an optical system 13 followed by a transducer 14 converting light flux into an electric signal 15 the magnitude of which is dependent on the light beam angle of incidence. A change in the signal 15 may be used correctively by acting on an electron beam deflecting coil 16. In Figs. 2, 2a, the light beam, comprising a pencil of rays formed by a telescopic system controlled by a suitable stop, is directed on to a segmented base comprised by four light conductors 20. The free ends of the light conductors are associated with photo-resistances 21 of a Wheatstone bridge providing deviation signal voltages U x  and U y . To suit the shape of seams to be welded, the base segments of the conductors 20 may be shifted by servomotors. The circuit of Fig. 2 may be replaced by 1 including 4 solar cells (Fig. 3a, not shown). In Fig. 3b, these solar cells are arranged in chessboard fashion, connected-together surfaces 35x on one side of a central x axis being connected with connected-together surfaces 35x on the other side of the x axis to form an x bridge, and connected-together surfaces 35y on one side of a central y axis being connected with connectedtogether surfaces 35y on the other side of the y axis to form a y bridge. Fig. 4 is a bridge circuit (shown for an x bridge only) which comprises a multiplier 33, an amplifier 32 and a feed back loop, and provides comparison brightness compensation in respect of two solar cells 31x. In Fig. 4, the light beam brightness at 13 is stabilized by splitting the beam, by a prismatic beam splitter 41, into branches each passing through polarization filters 42a, 42b and a Kerr cell 43a, 43b. A photo-cell 44 following the second of the filters 42b acts, via a regulator 45, on the Kerr cells to provide an output to an electro-optical transducer 18 at the second of the filters 42a which is independent of brightness fluctuations. The Kerr cells may be dispensed with and the filters relatively rotated. In Fig. 5 (not shown), the light beam at 13 is directed on to a mirror (51) deflectable by a continuously operating sawtooth generator. The beam reflected by the mirror is projected on to a surface (52) having centred thereon an electro-optical transducer (53). When the reflected beam impinges on the transducer the sawtooth generator is zeroed. The welding point position is determined by the generator peak values. Welding joint position determination.-In one embodiment, a beam of light is directed on to the joint, and the reflection from the joint is supplied, through a filter suppressing beam welding point light, to an electro-optical transducer. In a further embodiment, the beam of light is scanned over the joint via a mirror deflectable by a sawtooth generator, and the reflected beam is supplied to an electro-optical transducer the signal from which zeroes the sawtooth generator. The welding joint position is determined by the generator peak values.